1. Field of the Invention
The present invention relates to a method of manufacturing composite moldings which are formed by adhering a desired skin material onto the surface of a plastic base material in order to give a decoration and a special function to composite moldings and to a die which is particularly recommended to carry out the method.
2. Description of the Related Art
Composite moldings can be exemplified by interior materials of automobiles or the like. Those composite moldings are ordinarily manufactured by adhering a skin material such as PVC leather, carpet, or the like having an advanced decoration performance onto a plastic molded article as a base material by using an adhesive agent.
However, the above manufacturing method, requires much labor to adhere the skin material. Thus, there are problems such that designs are limited, the defect rate of products is high and manufacturing costs are high.
Therefore, there has also been proposed a method wherein a special stamping molding machine is used, a skin material is previously adhered on the inner surface of a die, and after that, a fused resin is injected into the die, and the die is clamped, thereby obtaining composite moldings covered with the skin material.
However, in such a kind of conventional well-known stamping molding machine, simultaneously with the start of the injection of the fused resin, contact of a part of the resin with the skin material is immediately started. However, the skin material is completely covered by the resin at the time of the completion of the die clamping. Therefore, the contact time between the resin and the skin material changes depending on the portion on the skin material and the temperature of the resin upon contacting also varies depending on a location. Consequently, there is a problem such that in the case of particularly, obtaining large moldings, uniform moldings cannot be obtained.
More particularly, near a resin injection gate, the injected high temperature resin directly collides and comes into contact with the surface of the skin material at a high pressure. However, in a portion away from the gate, when the die clamping is performed, the resin comes into contact with the skin material at relatively low temperature and low pressure.
Therefore, thicknesses or densities of composite moldings are uneven and exhibit wrinkles, a variation of brilliance, or the like on the surface, so that composite moldings of a good quality are not obtained.
To solve the above problems, there has been proposed a stamping molding machine which executes the molding after a fused resin is almost uniformly injected and coated onto the surface of a skin material. However, the above machine has problems in that it is expensive, has a long molding cycle and resins which can be used are limited. In addition, the problem that the temperature of the resin upon molding is uneven is not completely solved.